Method for rigless zone abandonment using internally catalyzed resin system

ABSTRACT

A zone of a subterranean formation penetrated by a well bore is permanently plugged by injecting a liquid resin system containing at least one thermosetting resin and at least one curing agent or catalyst therefor into the formation and injecting into the wellbore following the resin system, a second liquid containing at least one chain stopping compound to react with one component in the resin system to prevent any of the resin system remaining in the well bore from crosslinking to a sufficient crosslink density to form a solid in the wellbore. Preferably, the second liquid also contains a fluid loss additive to minimize loss of the second liquid from the wellbore to the formation. The method permits a zone to be plugged off and abandoned without the need to erect a drilling rig to drill out excess plugging material remaining in the wellbore. In a preferred embodiment, the resin system comprises the diglycidyl ether of bisphenol A and polymethylene phenylamine in ethylene glycol ethyl ether, and the preferred second liquid is monoethanolamine in ethylene glycol ethyl ether as a solvent with ethylcellulose and silic flour to control fluid loss.

I. BACKGROUND OF THE INVENTION

A. Field of the Invention

The present invention relates to a method for plugging a zone of asubterranean formation penetrated by a wellbore. More particularly, itrelates to a plugging technique utilizing a resin system containing athermosetting resin and a curing agent or catalyst therefor in a singletreatment stage. Another aspect of the invention is a treating fluidwhich may be utilized in one embodiment of the method.

B. Description of the Prior Art

In the production of oil and gas from subterranean formations, it isoften found that water is produced with the hydrocarbons. Varioustechniques are known to selectively alter the permeability of theformation to improve the production of hydrocarbons relative to theproduction of water. Such techniques are not always successful however.Some may prove effective for a period of time, but eventually, the ratioof water:oil produced may become so high that production from thatinterval is no longer economically practical. In other instances, thewater production may be so severe even initially that selective pluggingtechniques are not effective. When any of these conditions exists, it isdesirable to plug that zone of the formation completely and permanently.Frequently, however, it is desired to produce from the same well at adifferent depth.

Various techniques have been proposed for permanently plugging a zone ofa formation.

One technique which has been employed is to squeeze a cement slurry intothe formation opposite the perforations adjacent the formation zone tobe plugged. This technique requires waiting for the cement to set andthereafter drilling out the set cement remaining in the borehole.Furthermore, since the cement slurry contains a large amount ofparticulate material, it is not possible to obtain much depth ofpenetration into the formation.

Basically three approaches to chemically plugging a zone have beenproposed. One approach is to consecutively inject into the formation,materials which react in situ to form a plug. A serious drawback of thistechnique, however, is that it is difficult to assure adequate mixing ofthe reactants since at least to some extent, one fluid tends to displaceanother within the formation rather to mix with it. A second approach tochemical plugging is to inject materials which will react with formationsubstances such as brine, sand particles, clays, or other materialsnaturally present in the formation. Again, however, the reliability ofsuch techniques has not always been completely satisfactory.

The third basic approach to chemically plugging a formation has involvedinjecting previously mixed materials--e.g. a resin system containingboth resin and a crosslinker or catalyst therefore in a singlestage--into the formation where conditions such as time, temperature,and/or pressure will trigger a plug-forming reaction. A serious drawbackof such systems, however, has been the need to come in with a drillingrig to clean out residual material which sets in the wellbore. Forexample, Robichaux, U.S. Pat. No. 3,308,884 teaches use of an aminecatalyzed epoxy resin system for such a plugging operation, but teachesat column 7, lines 54-61 that after the resin has set, the remainingresin in the borehole can be drilled out and further drilling of thewell can be resumed. The need to drill the material out of the well boresignificantly increases the cost of a treatment because of the need toerect a drilling rig--especially where an offshore well is involved.

II. SUMMARY OF THE INVENTION

The present invention is a method for permanently plugging a zone of asubterranean formation penetrated by a wellbore. In carrying out themethod, a resin system containing at least one thermosetting resin andat least one curing agent or catalyst for the resin is injected into theformation via the wellbore. The resin system is displaced into theformation by a second liquid containing an effective amount of at leastone chain stopping compound to react with at least one component of theresin system. Preferably, the second liquid also contains a fluid lossadditive. The chain stopping or set inhibiting stage may be separatedfrom the resin stage if desired, e.g. by a wiper plug, and is injectedin a manner so that substantially none of the set inhibiting stage isitself injected into the formation. Reaction of any of the resin systemremaining in the wellbore is thereby capped before sufficiently highcrosslink density is achieved to form a solid residue in the wellbore.The liquid remaining in the wellbore can be removed at a later time,e.g. by recirculation to the surface, bailing, displacement into anotherzone, and the like. The resin system injected into the formation curesto form a consolidated mass which is substantially impermeable.

The present invention permits a zone to be plugged and abandoned withoutthe need for drilling out residual material left in the wellbore, makingthe invention particularly attractive for use in wells having aplurality of completion zones and for wells in remote locations whererig time is extremely costly.

III. FURTHER DESCRIPTION OF THE INVENTION

The resin system stage employed in the present invention is conventionaland may comprise any thermosetting resin and a suitable curing agent orcatalyst appropriate for the resin employed, to provide a liquid systemwhich can be injected into the formation to be treated in a single stageand which will cure in the formation to substantially reduce thepermeability of the formation in the vicinity of the wellbore,preferably to a permeability of about 0.01 millidarcy or less. Sincesuch a resin system does not require a separate overflush or preflush toreact, such a resin system is sometimes referred to as "internallycatalyzed" in the parlance of the oilfield, though in practice most suchsystems employ a second polyfunctional monomer rather than a catalyst inthe literal sense of the term catalyst. Thus, suitable resin systemsbased on phenolic resins, furan resins, furfural alcohol resins, vinylester resins, and the like may be employed as those skilled in the artwill appreciate. However, epoxy resin type systems are preferred. Epoxysystems are generally more readily compatible with water likely to bepresent in the formation, and once set, have excellent chemicalstability under typical formation conditions. Numerous embodimentsaccording to the present invention are available using epoxy systemswhich give excellent performance using materials which are readilyavailable at reasonable cost and which with routine precautions, arerelatively safe to workers, to equipment, and to the environment duringtransportation, storage, and use. Accordingly, the invention will bemore particularly described with reference to epoxy based systems,though it is to be understood that the invention is not to be limitedthereby.

Epoxy resins suitable for use in the present invention comprise thoseorganic materials possessing more than one epoxy group. Examples of thepolyepoxides include 1,4-bis(2,3-epoxypropoxy) benzene,1,3-bis(2,3-epoxypropoxy) benzene, 1,4'-bis(2,3-epoxypropoxy) diphenylether, 4,4'-bis(2-methoxy-3,4-epoxybutoxy) diphenyl dimethylmethane, and1,4-bis(2-methoxy-4,5-epoxypentoxy) benzene.

Other examples of resins suitable for use herein are glycidyl-type epoxyresins such as those described by Lee et al. in Handbook of EpoxyResins, McGraw-Hill, 1967, Chapter 2.

Specific examples include the epoxy polyethers of polyhydric phenolsobtained by reacting a polyhydric phenol with a halogen-containingepoxide of dihalohydrin in the presence of an alkaline medium.Polyhydric phenols that can be used for this purpose include resorcinol,catechol, hydroquinone, methyl resorcinol, or polynuclear phenols, suchas 2,2-bis(4-hydroxyphenyl) propane (bisphenol A),2,2-bis(4-hydroxyphenyl) butane, 4,4'-dihydroxybenzophenone,bis(4-hydroxyphenyl) ethane, 2,2-bis(4-hydroxyphenyl) pentane, and1,5-dihydroxynapthalene. The halogen-containing epoxides may be furtherexemplified by 3-chloro-1,2-epoxybutane, 2-bromo-1,2-epoxyhexane,3-chloro-1,2-epoxyoctane, and the like. Such polymeric products may berepresented by the general formula: ##STR1## wherein each A isindependently a divalent hydrocarbon radical having from 1 to 6 carbonatoms, --S--, --S--S--, ##STR2## each X is independently hydrogen, analkyl group of from 1 to 6 carbon atoms, chlorine or bromine, m has avalue of zero or 1, and n has an average value from zero to about 20.

The above-described preferred glycidyl polyethers of the dihydricphenols may be prepared by reacting the required proportions of thedihydric phenol and the epichlorohydrin in the presence of a causticsuch as sodium hydroxide or potassium hydroxide to neutralize thehydrochloric acid formed during reaction. The reaction is preferablyaccomplished at temperatures within the range of from 50° C. to 150° C.The heating is continued for several hours to effect the reaction andthe product is then washed free of salt and base.

Another group of polyepoxides that may be used comprises the glycidylethers of novolak resins, polynuclear polyhydroxy phenols, which areobtained by condensing an aldehyde with a polyhydric phenol in thepresence of an acid catalyst. Further prepartation of novolak resins isdescribed by T. S. Carswell in Phenoplasts, page 29 et seq. (1947).Typical members of this class are represented by the formula: ##STR3##wherein each R is independently hydrogen or an an alkyl group from 1 to4 carbon atoms, each X is independently hydrogen, an alkyl group of from1 to 6 carbon atoms, chlorine, or bromine, and n has an average value offrom 0 to about 20.

A number of curing agents are known which harden unset epoxy resins. Seegenerally Chapters 5 through 12 of the Lee et al. text. Specific classesof curing agents include, for example, amines, dibasic acids and acidanhydrides. The preferred hardening agents are the amines, especiallythose having a plurality of amino hydrogen groups. Included arealiphatic, cycloaliphatic, aromatic or heterocyclic polyamines, such asdiethylene triamine, ethylene diamine, triethylene tetramine,dimethylamino propylamine, diethylamino propylamine, piperidine, methanediamine, triethyl amine, benzyl dimethylamine, dimethyl amino methylphenol, tri(dimethylaminomethyl) phenol, a-methylbenxyl dimethylamine,meta-xylene diamine, 4,4'-dimethylenedianiline, polymethylenepolyphenylamine, pyridine, and the like. Mixtures of various amines maybe employed. The amines or other curing agent react rather slowly toconvert the polyepoxides to an insoluble form. A suitable curing agentand concentration thereof best suited for a particular well can easilybe determined by a knowledge of temperature conditions and availableworking time, i.e. length of time between adding the curing agent andfinal positioning of the resin-containing mixture in the formation.

The curing agent can be employed in an amount ranging from about 40 tomore than about 125 percent, preferably about 70-110 percent and morepreferably about 85-100 percent, of that stoichiometrically required.

Preferably, the resin and curing agent are admixed in a mutual solventto provide a solution which is easily pumped and which can be readilyinjected into the formation. Too much solvent, however, can result inincomplete plugging or prolonged cure times. Those skilled in the artwill be able to select a suitable solvent and solvent ratio depending onthe choice of resin and curing agent. For example, for epoxy systems,suitable diluents are discussed generally in Chapter 13 of the Lee etal. text hereinabove cited. The solvent may be, for example, an organicalcohol, ester, ether, ketone, acetate, etc., and mixtures thereof.Specific solvents include, for example, 2-(2-ethoxyethoxy)-ethanol,ethyl acetate, amyl acetate, methyl ethyl ketone, methylisobutyl ketone,xylene, ethylene glycol, n-butyl ether, alkylene glycol alkyl etherssuch as ethylene glycol ethyl ether, diethylene glycol isobutyl ether,and the like. Specific examples of suitable combinations of solventsinclude xylene/ethylene glycol ethyl ether e.g. in a 1.5:1 to 0.3:1weight ratio, and toluene/ethylene glycol ethyl ether.

A most preferred resin system according to the present inventioncomprises about 20-65 weight percent ethylene glycol ethyl ether, mostpreferably about 20-30 weight percent, and the balance an approximatelystoichiometric blend of D.E.R. 331 brand epoxy resin, which is a liquidepoxy resin of the bisphenol-A/epichlorohydrin type having an averageepoxide equivalent weight of about 190, and Jeffamine AP22 brandpolymethylene polyphenylamine, which has an average --NH equivalentweight of about 51.5.

The second essential step in the present invention is the injection intothe wellbore of a liquid containing at least one chain stopping compoundto react with at least one component of the resin system to prevent anyresidual resin system material in the wellbore from setting up in thewellbore. Preferably, the second liquid includes a mutual solvent forthe resin system components, for the chain stopping compound, and forthe reaction product of the resin system components with the chainstopping compound.

A most preferred embodiment when employing the most preferred resinsystem hereinabove described is a 5 to 50 and more preferably 15-25weight percent solution of monoethanolamine in an alkylene glycol alkylether such as ethylene glycol ethyl ether. The concentration ofmonoethanolamine in the glycol ether is not sharply critical.Monoethanolamine itself is not a particularly effective cosolvent forthe partially polymerized epoxy monomer, so that use of lesser amountsof solvent may give a rather viscous fluid in the wellbore. The use ofgreater amounts of solvent is constrained only by practical limitationson treatment logistics such as the volume of the wellbore. Althoughmonoethanolamine has two --NH sites, when present in a suitable excess,reaction of the first hydrogen with the an epoxy functional group on theresin is so much more rapid than the reaction of the second site, thatthe monoethanolamine functions as a chain stopping compound by tying upthe reactive sites on the epoxy molecule, thereby preventing hardeningof the resin in the wellbore. Other primary and secondary monofunctionalamines (i.e. a single RNH₂ or R₂ NH group, optionally with nonreactivesubstiuents on R) may also be employed to cap the chain by reaction withthe epoxy sites, as may monobasic acids. Alternatively, the liquidemployed in the second step may contain a component to stop thecrosslinking reaction by tying up reactive sites on the crosslinker.Thus, for example, a monofunctional epoxy reactive diluent such as thosetaught in Chapter 13, pages 13-7 through 13-10 of the Lee et al. textmay be employed.

Those wishing to employ resin systems other than epoxy resins willreadily be able to select suitable chain stopping compounds appropriatefor the particular resin system employed.

Also, the liquid employed in the second essential step of the presentinvention preferably contains a fluid loss additive to minimize loss ofthe fluid from the wellbore into the formation. The invention may bepracticed without use of a fluid loss additive, provided care is used toavoid injecting too much of the chain stopping solution into thewellbore--or equivalently, over displacing a slug of the chain stoppingstage--so that a significant amount of the chain stopping materialenters the formation. Obviously, injection of significant quantities ofthe chain stopping fluid into the formation would interfere with thesetting of the resin in the formation, and should therefore be avoided.A suitable fluid loss additive is a mixture of a cellulose compoundwhich is soluble in the liquid of said second stage, and a finelydivided inert particulate in relative proportions such that fluid losscontrol is imparted to the fluid. By "soluble" in the context of thecellulose compound is meant sufficiently dispersible to form a stable,visually uniform dispersion at the concentration employed.Ethylcellulose and higher homologs which are water insoluble, organicsoluble cellulose derivatives, are preferred. A suitable inertparticulate is finely divided silica, i.e. silica flour. Preferably, theparticulate has a particle size diameter within the range of from about1 to about 100 microns.

Preferably, the set inhibiting liquid contains from about 0.2 to about4.5 percent of the cellulose derivative, e.g. ethylcellulose, and about0.04 to about 0.75 percent of the inert particulate, by weight of theliquid. Quantities near the upper ends of the ranges are generallyemployed where the formation is relatively permeable, whereas lesseramounts are satisfactory where the formation is relatively tight. Mostpreferably, from about 1.25 to about 3.3 percent of ethylcellulose andabout 0.18 to about 0.55 percent of silica flour are employed, e.g.about 100-300 lbs of an approximately 6 parts ethylcellulose to one partsilica flour mixture per 1000 gallons of fluid.

The following treatment according to the present invention has beenproposed to a well operator wishing to plug off a zone in an offshorewell producing water through perforations at a depth of 7758-7782 feet.The treatment can be carried out without use of a drilling rig. The wellis a multiple completion zone well equipped with a 7-inch, 26 lb/ftliner from 6207 feet to total depth, and the zone of interest isolatedby packers at 7628 ft and 7820 ft. After shutting off the perforationsat 7758-7782 feet, the well operator wishes to perforate at anotherdepth but still within the same area isolated by the packers at 7628 and7820 feet. 23/8-inch, 4.7 lb/ft EUE tubing extends from the surface tothe 7628 ft packer, and another tubing string of the same size extendsthrough the zone of interest to another zone below the 7820 ft. packer.

To divert treatment fluids from that portion of the liner extending fromthe bottom of perforations to the top of the lower packer, 1.25 bbls ofheavy brine (e.g. 11 lb/gal calcium chloride brine) is first spotted inthe wellbore through coil tubing. To clean the formation, 500 gallons ofa 50:50 15% HCl:xylene acid dispersion as taught in U.S. Pat. No.3,794,523 is injected and displaced with 40 bbls filtered sea water and10 bbls of diesel oil. Although not essential, the diesel oil or similarhydrocarbon displacement fluid will be employed because the working timeof the particular resin system is shortened somewhat by contact withfresh water, sea water, or acid. Alternatively, a lower alkyl alcoholmay be used in lieu of part or all of the diesel oil. The foregoingoptional steps are not part of the invention per se, but are recommendedto clean the formation and thereby achieve optimum sealing performance.

The resin system is to be prepared by bringing to the well site, asolution of 80 weight percent D.E.R. 331 brand epoxy resin and 20percent ethylene glycol ethyl ether, and another solution of 60 weightpercent Jeffamine AP22 brand polymethylene polyphenylamine in 40 percentethylene glycol ethyl ether. The resin system is to be prepared byadding 0.4 parts by volume of the polymethylene polyphenylamine solutionto 1 part of the epoxy resin solution and admixing same for about 10-15minutes. Seventeen hundred gallons of the above mentioned internallycatalyzed resin system--enough to penetrate radially at least aboutthree feet around the wellbore over the perforated interval--is to beinjected down the tubing and displaced into the formation with 500gallons of a mixture of 1 part by weight monoethanolamine, 4 parts byweight ethylene glycol ethyl ether, and 150 pounds of a 6:1 weightmixture of ethylcellulose and silica flour. Finally, the set inhibitingfluid may be displaced to depth with 22.8 bbls of filtered seawater, ora sufficient lesser volume to balance the formation pressure. The resinsystem may, if desired, be separated from the set inhibiting fluid by awiper plug to wipe the tubing substantially clean from the surface tothe 7628 foot packer and also to minimize mixing of the set inhibitingfluid with all but the final portion of the resin system. Using thewiper plug, the theoretical minimum volume of set inhibiting liquid tobe employed would be the volume between the packer at 7628 feet wherethe wiper plug would fall free and the surface of the heavy brineinitially spotted below the perforations. However, an excess ispreferably employed to assure an adequate volume to contact exposed wellequipment. In lieu of the filtered seawater, other suitable displacementfluids may be employed for the final displacement such as diesel oil,nitrogen, and the like. The well will then be shut in for about 12 hoursto permit the internally catalyzed resin system to set up in theformation, after which time coil tubing will be inserted and theisolated portion of the well flushed clean. The new zone will then beperforated at the new location desired by the operator and conventionalstimulation and sand control treatments carried out through the newperforations.

What is claimed is:
 1. A method for permanently plugging a zone of asubterranean formation penetrated by a wellbore comprising:(a) injectinginto the formation via the wellbore, a liquid resin system comprising ina single stage, at least one thermosetting resin and at least one curingagent or catalyst for said resin so that said resin system cures afterplacement in the formation, and (b) injecting into the wellborefollowing said resin system, a second liquid containing an effectiveamount of at least one chain stopping compound to react with at leastone component of the resin system to prevent portions of the resinsystem contacted by said second liquid from crosslinking in the wellboreto a sufficient crosslink density to form a solid in the wellbore, saidinjecting of said second liquid being carried out so that substantiallynone of said second liquid is displaced into the formation.
 2. Themethod of claim 1 wherein the resin system is an epoxy resin system. 3.The method of claim 2 wherein the epoxy resin is a glycidyl-type epoxy.4. The method of claim 2 wherein the curing agent contains a pluralityof amino hydrogen groups.
 5. The method of claim 2 wherein the secondliquid comprises a monoepoxy-containing diluent substantially free ofother reactive sites.
 6. The method of claim 2 wherein the second liquidcomprises a monofunctional primary or secondary amine.
 7. The method ofclaim 6 wherein the second liquid comprises a non-reactive solvent andan alkanol primary amine.
 8. The method of claim 7 wherein the solventis an alkylene glycol alkyl ether and the amine is monoethanolamine. 9.The method of claim 8 where the resin is the diglycidylether ofbisphenol A and the curing agent is an aromatic polyamine.
 10. Themethod of claim 7, 8, or 9 wherein the second liquid also contains ablend of an organic soluble, water insoluble cellulose derivative and afinely divided inert particulate in a ratio and quantity effective toprovide fluid loss control to said second liquid, thereby substantiallypreventing loss of said liquid from the borehole to the formation. 11.The method of claim 10 wherein the cellulose derivative isethylcellulose and the inert particulate is silica flour.
 12. The methodof claim 1, 2, 3, 4, 5, 6, 7, 8, or 9 wherein the second liquid containsa fluid loss additive to reduce the loss of said liquid from theborehole to the formation.